This application claims priority from Brazilian Patent Application No. P10100680-0, filed Feb. 21, 2001.
1. Field of the Invention
This invention relates to a cracking catalyst composition and its use.
2. Prior Art
Typical fluid catalytic cracking (FCC) catalysts comprise a zeolite component. One of the problems frequently encountered in FCC is poisoning of the zeolite by deposition of metals, e.g. nickel and vanadium, which are present in many hydrocarbon feeds that need to be cracked.
One way of dealing with this problem is protection of the zeolite by way of using metal scavengers. Broadly, metal scavengers may contain alkaline earth metal compounds, such as magnesium, calcium, and barium, or clays rich in rare-earth metal compounds. These metal scavengers can be present in the FCC catalyst particles or in separate additive particles, i.e. a physical mixture of FCC catalyst and additive particles. The advantage of using metal scavengers in separate additive particles is that the scavenged metals are kept farther away from the zeolite.
U.S. Pat. No. 5,965,474, incorporated by reference herein, discloses a catalyst composition comprising a conventional faujasite-containing FCC catalyst and an additive comprising a M41S material and incorporated within its pores a metal passivator selected from a rare earth compound, an alkaline earth metal compound, or a combination thereof. M41S material is defined in this reference, as well as in the present specification, as being a non-layered ultra large pore crystalline material exhibiting after calcination an X-ray diffraction pattern with at least one peak at a position greater than about 18 Angstrom Units d-spacing with a relative intensity of 100 and a benzene adsorption capacity of greater than about 15 grams benzene per 100 grams anhydrous crystal at 50 torr and 25xc2x0 C. An example of an M41S-material is MCM-41.
The catalyst composition according to this document has several drawbacks. First, the preparation of M41S material requires organic templates, which are relatively expensive and can only be completely removed by calcination. Such removal precludes their recycling and leads to environmentally undesired emissions.
Second, M41S materials have relatively low thermal stability. For instance, Z. Luan et al. (J. Phys Chem. 99 (1995) pp. 10590-10593) have shown that structural aluminium is increasingly removed from the MCM-41 structure above 300xc2x0 C. Moreover, due to the relatively thin walls of these materials their structure readily collapses upon thermal treatment (N. Coustel, et al., J. Chem Soc., Chem. Commun., 1994, pp. 967-968). As FCC processes are generally conducted at elevated temperatures, additives with high thermal stability are desired.
Third, M41S materials have relatively low intrinsic acidity. Due to this relatively low acidity and their relatively low thermal stability, M41S materials have a much lower cracking activity than typical FCC catalysts. Hence, replacement of a part of the FCC catalyst by such additives results in dilution of the catalyst and hence in a reduction in cracking activity.
The present invention provides a cracking catalyst composition with good metal scavenging properties with less or without dilution of the cracking catalyst and having better thermal stability than M41S materials. Moreover, the composition is less expensive than systems based on M41S-materials.
In one embodiment, the present invention comprises a cracking catalyst composition comprising a physical mixture as separate particles of 10-90 weight % of a cracking catalyst A and 90-10 weight % of a cracking catalyst B, whereby catalyst A is a zeolite-containing cracking catalyst, and cracking catalyst B is a catalyst having a higher average pore volume in the pore diameter range of 20-200 xc3x85 than catalyst A in the same pore diameter range. The catalyst composition of the invention does not contain M41S material.
In another embodiment the present invention comprises the use of the above catalyst composition in the fluid catalytic cracking process.
Other embodiments of the invention comprise details including catalyst compositions and physical properties, particularly pore volumes.